Nick Raynsford, MP for Greenwich, south London, where the exhibition is due to be staged, said an incoming Blair administration would pump public money into the prestige scheme.
The Opposition construction spokesman's intervention came as the Millennium Exhibition appeared to be on the verge of collapse because of lack of commercial interest in it.
Government sources warned yesterday that unless agreement about the funding and management of the project is reached early in the new year, then it may have to be abandoned, or at least scaled down drastically.
One source said: "There is a chance it will all fold." Time is also running out to get the exhibition dome built by 2000.
Mr Raynsford, the Opposition construction spokesman, is to meet key figures over the next few days to pledge "additional underpinning from the public sector". He said: "We are coming up with sensible proposals that will enable the project to succeed.
"The Millennium Exhibition is an important event, and it must go ahead. But there must be a clear budget and a clear management structure, not just because we expect to inherit it. A project of this size with a very tight timetable is inevitably open to the serious risk of cost overruns.
"No responsible opposition could give a blank cheque as the Government has been asking. We want to see a realistic budget, and we recognise there will almost certainly be a need for some additional underpinning from the public sector."
Staff working on the Millennium project and sources within the Government believe that without Labour's intervention the project is lost. A Government source said: "The big issue is seeing that we get Labour on board."
Unless Labour "delivered something concrete", said the source, and committed itself to the project before the end of next month, the entire showpiece exhibition would be immediately "scaled down or completely abandoned".
They have also argued that the exhibition might never be staged if Labour refuses to extend Lottery funding in the event of winning the general election, an extraordinary half-admission that the Conservatives will be out of office within months.
Time is also running out for construction of the exhibition building. The Government is planning to accept full financial responsibility for the Millennium Exhibition, turning the organising company, Millennium Central, into a public body.
The Independent on Sunday has learned that materials and other orders for the massive dome complex on the Greenwich peninsula, designed by the award-winning architect Sir Richard Rogers, will have to be placed before the end of January to ensure they are delivered on time.
Among those Mr Raynsford will meet is Roger Freeman, the Minister for Public Service who is to become the Cabinet's "troubleshooter" and take overall charge of the project, which will become a publicly owned quango. Only pounds 150m has been guaranteed by the private sector.
Jennifer Page, chief executive of the Millennium Commission, is expected to take over as head of Millennium Central following the resignation of Barry Hartop. His departure was described by one insider as a "blow".
Imagination, the London-based design consultancy which will design, with sponsors, the interior of the Millennium Exhibition, said yesterday that although a lot of work on the project has been done, nothing had yet been finalised. A spokesman said: "Every day that goes by is now a day that we would have liked to have been working on this project. As we've said before, this is one event that cannot open late."Reuse content